This invention relates to a reduction gear mechanism having a magnet clutch mechanism therein and comprising a worm and a worm wheel.
Conventionally, automobiles and the like vehicles commonly employ an electric motor as a source of a driving force to automatically operate various devices and apparatus provided therein.
In such conventional automobiles, a final reduction gear comprising a worm and a worm wheel in combination is used to multiply output torque of the motor. A clutch is interposed between the motor and the final reduction gear which is operable to connect and disconnect transmission of power between them.
FIG. 1 illustrates an example of such a construction, which comprises a motor (a), a clutch (b), a final reduction gear (c) comprising a worm and a worm wheel in combination, and an output power shaft (d).
This construction, however, is disadvantageous in that it requires a large spacing for installation.
Besides, the combination of a worm and a worm wheel has a deficiency that it does not allow a reverse operation thereof from its output side. Accordingly, even if the clutch is disengaged to stop an automatic operation, it does not result in availability of a manual operation from the output side.
If the construction is modified to increase the lead angle of the worm to reduce the reduction ratio of the reduction gear mechanism, it will enable a reversing operation of the reduction gear mechanims from its output side. But, such modification will not lead to a smooth reversing operation of the reduction gear mechanism since such a reversing operation will be opposed by a load arising at the reduction stage. Also, such modification will result in an employment of a larger motor to meet the requirement of larger torque.